Re: VFD Selection

Leslie,
I currently do not have a precision mill (only a hobby inaccurate
mill). I plan to use my current hobby mill to create my more precise
gantry mill and for this I need to make many holes in mild steel. Do
you have a picture of your spindle? For milling mild steel, I will
need a spindle/motor that runs at 800 - 1200 rpm approximately.
Thanks,

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Leslie M. Watts"
<leswatts@a...> wrote:

> A small VFD as I am typically familiar with runs from single phase

or 3

> phase
> (usually 240v) and puts out a 3 phase 240v suitable for driving an

induction

> motor. The frequency is variable over a wide range to control the

rpm

> of the motor. They could be designed to work with lower voltages,

but 120vac

> is not used much due to limited power and increased i^2r heating.
>
> I guess the keywords here are CUT STEEL. You sure don't want to try

that

> with
> the router...it's not built for it.
>
> Using the shaft of a typical motor as a spindle likewise is not

designed

> for those forces.
>
> I do think I have a design for a belt driven angular contact or

tapered

> roller bearing spindle that could be run from a single phase 120vac

motor

> at fixed speed (least costly), a dc motor/servo amp, or a phase

control

> (voltage)
> dc motor over a limited rpm. It would have torque due to the

gearing down.

> I could try and find it for you if you have the capability to do

precision

> (+/-0.0002") machining with your tools.
>
> Could you tell me more about what you want to cut and how fast?

Sounds

> like we are getting more into Milling machine territory. A steel

cutting

> gantry type machine is usually not in the hobby relm.
>
> Les
>
>
>
> Leslie M.Watts
> L M Watts Furniture
> Tiger Georgia USA
> (706) 212-0242
> http://www.lmwatts.com
> Engineering page:
> http://www.lmwatts.com/shop.html
> CNC surplus for sale:
> http://www.lmwatts.com/forsale.html
> CNC carved signs:
> http://www.lmwatts.com/signwp.html
>
>
>
>
> -----Original Message-----
> From: george_barr [mailto:george_barr@y...]
> Sent: Tuesday, April 13, 2004 4:28 PM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: [CAD_CAM_EDM_DRO] Re: VFD Selection
>
>
> Leslie,
> It appears that I cannot use a VFD or Variac to reduce my router

to

> 1k rpm. What type of motor can I use with a VFD (input: 120VAC,
> output: 120VAC or DC) without getting too expensive or without using
> servo drives? Is there a specific phase specification. Does the
> motor have to be AC or can it be DC? What I am planning to do is

cut

> mild steel (which requires low rpm speed)?
>
> Thanks,